The present invention generally relates to optical communication and, more particularly, to a photodetector device and a method of fabricating the same.
Digital modulation is generally used to transmit large amounts of data such as audio, video, voice, graphical and other media. The use of digital modulation requires a reliable and rapid data carrier means. The Internet, over which large amounts of information is now transmitted, has proven to be a cost effective and ubiquitous medium for data transmission. At its inception, the Internet was based on telephonic communications, which were in turn based on wire connections and electrical switching. The great amount of digital data used by multi-media has required the use of higher capability and higher speed transmission media. Optical fiber cable has proven to be an ideal backbone for the Internet because it has a large bandwidth and may carry much more data than wire/cable. Furthermore, optical fibers are low cost, flexible and are not sensitive to electromagnetic interference EMI.
There are many electro-optical applications, such as optical telecommunications and chip interconnects, that involve transmitting optical signals and converting the optical signals to electrical signals at high data rates. Generally, an optical source, i.e. transmitter, converts an electrical signal, either digital or analog, to a modulated light beam which is then passed through an optical fiber to an optical detector, i.e. receiver, that extracts an electrical signal from the received light beam. In today's rapidly advancing optoelectronics industry, vertical cavity surface emitting lasers (“VCSELs”) are preferred as optical sources, which may typically emit light having a wavelength of 850 nm (nanometer), 1310 nm, 1550 nm or other wavelengths. The systems available for performing such transmission and conversion usually require a photodetector compatible with the speed and bandwidth of the optical signal. The typical photodetectors are III-V family PIN (p-type/intrinsic semiconductor material/n-type) semiconductor detectors. A photodetector is capable of detecting light emitted by the VCSEL.
Optical sources that emit light having a wavelength of 850 nm are generally used in short-haul applications such as short range links in a metropolitan area. For an infrared optical source having a wavelength of approximately 850 nm, light emitted therefrom may reach down to 16.7 μm (micrometer) in depth into a silicon substrate. A conventional photodetector device where electrodes are formed on a substrate surface may not effectively absorb photo-generated carriers, in particularly those generated in a deeper region of the substrate. As a result, when a light pulse occurs, photo-generated carriers not absorbed are in a drift state, disadvantageously resulting in a lower optical current and a smaller bandwidth. Furthermore, photo-generated carriers in the drift state may cause the photodetector device to incorrectly detect the logical level, i.e., 0 or 1 of an optical signal. To avoid the risk of incorrect detection, high density light signal pulses may not be accepted, which potentially aggravates the entire system speed.